The invention relates to a gas chromatograph having a temperature-controlled injector.
Gas chromatographs may have different types of injectors for material to be investigated by gas chromatography, for example cold injection units, thermodesorption units, split units, traps (cryotraps), which require cooling in certain phases of operation in order, for example, to bring about adsorption of material to be investigated and/or prevent desorption thereof.
For example, German Patent 34 48 091 C3 discloses a cold injection unit in which an injection needle is used to deliver material to be investigated into a vaporizer tube which is connected via a transfer line to a capillary chromatography column. The vaporizer tube is surrounded by a heating unit in the form of a coiled resistance heater which is arranged inside a covering leaving a gap. On the outside of the covering there is provided a Peltier thermoelectric element for cooling. Apart from the fact that only a relatively small Peltier element with correspondingly low power can ordinarily be used for reasons of space, also the heat transmission to the vaporizer tube is poor, the temperature profile is uneven, and the reaction time is too long.
The alternate possibility of employing cryocooling would, apart from the disadvantages associated therewith in relation to the storage of coolant, lead to nitrogen or carbon dioxide, which are used in this case, getting from the gap between the coiled heating unit and covering into the oven chamber, which contains the capillary column, of a gas chromatograph and adversely affecting the programmed temperature and desired temperature profile prevailing therein.
It is an object of the preferred embodiments of the invention to provide a gas chromatograph provided with a cooling unit which makes it possible to cool a temperature-controlled injector with a rapid reaction time and a required temperature profile.
An example of a preferred embodiment of the invention concerns a gas chromatograph, comprising:
a temperature-controlled injector provided with a heating unit for heating the injector and a cooling unit concentrically surrounding the heating unit for cooling the injector;
wherein the cooling unit has a cooling coil which surrounds the heating unit and which cooling unit is provided via a feed line and a return line with an external source of liquid, cooled coolant, and
wherein a pump for circulating the coolant and a drain valve for draining the cooling coil are provided. Further objects, advantages and embodiments of the invention are evident from the following description.
The invention is explained in more detail hereinafter by means of an exemplary embodiment of the invention shown in the attached drawings.